U.S. patent number 5,918,977 [Application Number 08/875,441] was granted by the patent office on 1999-07-06 for method and plant for mixing and analyzing unhomogeneous flowable foodstuff, fodder or pharmaceutical material.
This patent grant is currently assigned to Wolfking Danmark A/S. Invention is credited to Claus Borggaard, Hilmer Jensen, Freddy Petersen, Jens Havn Thorup.
United States Patent |
5,918,977 |
Borggaard , et al. |
July 6, 1999 |
Method and plant for mixing and analyzing unhomogeneous flowable
foodstuff, fodder or pharmaceutical material
Abstract
The present invention relates to a method of mixing
inhomogeneous flowable food material, fodder material, or
pharmaceutical material in a tank provided with mixing devices. The
method comprises measuring and registering the content of one or a
number of components in samples taken from the material in the
tank.
Inventors: |
Borggaard; Claus (Viby Sj.,
DK), Petersen; Freddy (Jyllinge, DK),
Jensen; Hilmer (Sk.ae butted.lsk.o slashed.r, DK),
Thorup; Jens Havn (K.o slashed.benhavn N, DK) |
Assignee: |
Wolfking Danmark A/S (Slagelse,
DK)
|
Family
ID: |
8090383 |
Appl.
No.: |
08/875,441 |
Filed: |
August 21, 1997 |
PCT
Filed: |
February 09, 1996 |
PCT No.: |
PCT/DK96/00065 |
371
Date: |
August 21, 1997 |
102(e)
Date: |
August 21, 1997 |
PCT
Pub. No.: |
WO96/24843 |
PCT
Pub. Date: |
August 15, 1996 |
Foreign Application Priority Data
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|
|
|
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Feb 10, 1995 [DK] |
|
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0155/95 |
|
Current U.S.
Class: |
366/140 |
Current CPC
Class: |
G01N
15/02 (20130101); B01F 7/04 (20130101); G01N
21/359 (20130101); G01N 21/3563 (20130101); B01F
15/0267 (20130101); B01F 15/0289 (20130101); B01F
15/00785 (20130101); B01F 7/00158 (20130101); B01F
7/00275 (20130101); B07C 2501/0081 (20130101) |
Current International
Class: |
G01N
33/15 (20060101); G01N 15/02 (20060101); G01N
21/35 (20060101); G01N 33/02 (20060101); G01N
21/31 (20060101); B01F 015/00 () |
Field of
Search: |
;366/140,152.1,151.2,159.1,136,137 ;73/61.82,863.81 ;426/231
;356/440,441,442 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
2 137 340 |
|
Oct 1984 |
|
GB |
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WO 81/02467 |
|
Sep 1981 |
|
WO |
|
WO 83/02158 |
|
Jun 1983 |
|
WO |
|
Other References
Reichert et al. "Kostenersparnis bei der Fertigung von Wurstwaren
durch programmgesteuerte Rezepturoptimierung", Fleischerei-Technik,
1993, vol. 44(6), pp. 438-440, pp. 443..
|
Primary Examiner: Soohoo; Tony G.
Attorney, Agent or Firm: Pennie & Edmonds LLP
Claims
What is claimed is:
1. A method of mixing a flowable material, which comprises:
a) placing at least one unhomogeneous food, fodder or
pharmaceutical material having a form or size that can lead to
uneven component measurement into a tank provided with mixing
devices;
b) measuring and registering the content of at least one component
from samples taken from the material in the tank by removing
material from the tank through a tube which is situated adjacent
the tank and which communicates with the internal space of the
tank;
c) moving the removed material to a segment of the tube adapted for
making measurements;
d) measuring the effect caused by the material placed in said tube
segment on electromagnetic energy made to enter the tube while the
material is retained therein;
e) repeating steps c-d, optionally while introducing completely or
partly new material in the tube segment; and
f) registering at least one measurement value from the individual
measuring procedure to determine the content of the components to
be mixed.
2. The method according to claim 1 wherein the content of at least
one component of the material in the tank is determined by
repeating steps c-d after introducing new material into the tube
segment, and repeating the process until a representative sample is
tested.
3. The method according to claim 1 wherein the material is
introduced into the tube segment, and is returned to the tank at a
distance from the opening serving for removing material from the
tank after analysis.
4. The method according to claim 1 wherein steps c-d are carried
out while the material is being mixed in the tank.
5. The method according to claim 1 wherein the material is brought
to rest in the tube segment prior to carrying out the
measurement.
6. The method according to claim 1 wherein the material present in
the tube segment is compressed before the measurement is carried
out.
7. The method according to claim 1 wherein at least one form of
electromagnetic energy comprising microwaves of frequencies in the
interval between about 300 MHz and about 300 Ghz, single-energy,
dual energy or multi-energy, X-ray, or near-infra-red radiation is
used.
8. The method according to claim 7 wherein, if microwaves are used,
the tube segment is configured in the shape of a microwave guide,
and then one of attenuation, phase shift or time delay of the
microwaves is measured in the tube segment, if X-rays are used,
then attenuation of X-ray radiation transversely through a material
contained in the tube segment is measured, or if near-infra-red
radiation is used, then transmittance or absorbance of a material
contained in the tube segment is measured in the near-infra-red
interval (NIT).
9. The method according to claim 8 wherein measuring of the
transmittance or absorbance of the material placed in the tube
segment is conducted at a number of wavelengths in the interval
between about 700 and about 2400 nm; and the content of at least
one of the measuring values is registered.
10. The method according to claim 1 wherein the measuring values
are used to ascertain when the mixture in the tank is sufficiently
homogenous to allow the mixing process to be terminated and the
material discharged from the tank or subjected to a succeeding
processing step.
11. The method according to claim 1 wherein the content of at least
one component of the material is determined on the basis of at
least one of the registered measuring values, and the results are
shown on a display unit or used for controlling a dosage control
unit associated with the tank and adapted to add a quantity of a
component to the material in the tank.
12. The method according to claim 1 wherein, the transmittance or
absorbance of a particulate material with an average particle size
between 2 and 30 mm, is measured at a number of wavelengths in the
near-infra-red interval, after which at least one of the registered
measuring values is used to determine at least one of:
the content of at least one component of the material; or
the sufficiency of homogeneity of the mixture in the tank with
regard to at least one component such that the mixing process can
be terminated and the material discharged from the tank or subject
to a succeeding processing step.
13. A plant for mixing an inhomogeneous flowable food, fodder or
pharmaceutical material, comprising: a tank (2) for combining the
material, a plurality of mixing devices (4), an examining unit
adjacent the tank and comprising a tube (10) having an opening
communicating with the internal space of the tank (2) for removing
material from the latter, in said tube (10), a movable closure
member (17) situated in said tube adjacent the opening for
receiving material, a conveying member (18) for conveying material
having been removed through said opening into a segment (10b) of
said tube (10) adapted for carrying out measurements, a measuring
device (32-37; 40, 41; 50-56; 60-64) situated adjacent said segment
(10b) of said tube (10) and adapted to transmit electromagnetic
energy into said segment and to measure the influence on this
energy exerted by the material being present in said segment, a
control unit (6a) to cause the measuring procedure comprising the
introduction of completely or partly new material in said segment
(10b) and measuring of its influence on electromagnetic energy, to
be repeated, and a recording unit connected to said measuring
device and adapted to record individual measurement values or sets
of same for material having been measured in the respective
measuring procedures.
14. Plant according to claim 13, characterized in that said
measuring device comprises a light source (32,40) on one side of
said tube segment (10b) and a light receiver (36,41) on the
opposite side, and that the walls of the tube segment (10b) lying
in the path of rays between the light source and the light receiver
consist of a material (24) that is translucent for the wavelength
interval of the light to be examined, depending on the flowable
material, on which measurements are to be carried out.
15. Plant according to claim 14, characterized in that the light
source (32) and the light receiver (36) are of the wide-spectrum
type, and that a rotatable filter disc (34) is placed in the ray
path between the light source and the light receiver, said filter
disc (34) having a number of filters (35) situated at equal
distances from the axis of rotation of the disc and each adapted to
allow rays of a respective wavelength interval to pass, a motor
(37) on the shaft of said disc (34) being adapted to bring one
filter at a time into the path of rays.
16. Plant according to claim 14, characterized in that a number of
monochromatic light sources (40), each adapted to emit light in a
respective wavelength interval, is situated on one side of said
tube segment (10b), and that a light receiver (41) is situated on
the opposite side of said tube segment.
17. Plant according to claim 16, characterized by between 4 and 20
monochromatic light sources (40) in the form of laser diodes are
situated on one side of said tube segment (10b) and adapted to emit
light, each in a respective wavelength interval within the region
between 700 and 1200 nm.
18. Apparatus according to claim 13, characterized in that said
closure member (17) is adapted to be opened in connection with the
reception of material and to be closed in connection with the
conveying of material having been received into said tube segment
(10b) adapted for carrying out the examination.
19. Apparatus according to claim 13, characterized by a second
closure member (29) in the tube (10) on the side of said tube
segment (10b) opposite said receiving opening, said second closure
member (29) being adapted to be closed for a period while the
conveying member (18) conveys fully or partly new material into
said tube segment (10b) adapted for carrying out the examination,
and to open when the material having been examined is to be moved
out of said tube segment (10b).
20. Apparatus according to claim 13, characterized in that said
conveying member is a plunger (18) slidable in a fluid-tight manner
along the inside of said tube (10).
21. Apparatus according to claim 13, characterized by comprising
one or a number of pneumatic cylinders (14,27) with associated
pistons (15,16,28) adapted to actuate said conveying member (18)
and/or closure members (17,29) in said tube (10).
22. A method of mixing flowable material comprising:
a) placing at least one unhomogeneous food material, fodder
material or pharmaceutical material in a tank provided with mixing
devices;
b) measuring and registering the content of at least one component
in samples taken from the material in the tank;
c) removing material from the tank through a tube which is situated
adjacent the tank and which communicates with the internal space of
the tank;
d) moving the material to a segment of the tube adapted for making
measurements, where the measurement is carried out while the
material in the tube is at rest;
e) measuring the effect caused by the material placed in said tube
segment on electromagnetic energy made to enter the tube;
f) repeating the above steps c-e, optionally with the introduction
of completely or partly new material in the tube segment; and
g) registering at least one measurement value from the individual
measuring procedure.
23. A method of mixing flowable material comprising:
a) placing at least one unhomogeneous food material, fodder
material or pharmaceutical material in a tank provided with mixing
devices;
b) measuring and registering the content of at least one component
in samples taken from the material in the tank;
c) removing material from the tank through a tube which is situated
adjacent to the tank and which communicates with the internal space
of the tank;
d) moving the material to a segment of the tube adapted for making
measurements;
e) compressing the material present in the tube segment to a
pressure of between about 200 and about 2000 kPa (about 2 and about
20 bar);
f) measuring the effect caused by the material placed in said tube
segment on electromagnetic energy made to enter the tube;
g) repeating the above steps c-e, optionally with the introduction
of completely or partly new material in the tube segment; and
h) registering at least one measurement value from the individual
measuring procedure.
Description
TECHNICAL FIELD
The present invention relates to a method of mixing inhomogeneous
flowable food material, fodder material or pharmaceutical material
in a tank provided with mixing devices, said method comprising
measuring and registering the content of one or a number of
components in samples taken from the material in the tank.
BACKGROUND ART
Minced or comminuted meat, e.g. for use in hamburgers, is
traditionally produced from raw materials in the form of meat and
fat obtained when processing or trimming carcass cuts and the like.
The raw materials are coarsely comminuted down to a particle size
of 10-15 mm and are placed in respective tanks or tubs, of which
one e.g. contains pure meat and another one fat-containing meat or
possibly pure fat. The desired composition of the finished product
is provided by mixing the various types of meat and fat raw
material in predetermined ratios, so that the mixture will fulfil
certain specifications with regard to fat, protein etc. When the
correct ratio has been achieved, the raw materials are mixed in the
best possible manner without spoiling them by "overmixing". Then,
the mixture is discharged from the tank and finally comminuted to
the desired particle size, after which the product is used for
making hamburgers, sausage meat or other products.
Especially the fat content in the raw materials can vary
considerably, and for this reason it is necessary to determine the
fat content once or a number of times to ensure that the finished
product fulfils the specifications. Either a direct or an indirect
method may be used to ensure that the finished product has the
specified fat content.
The direct method consists in that the operator, on the basis of
her or his experience, will introduce the various types of raw
materials in the mixer in proportions estimated to make the mixture
contain a surplus of meat. When the ingredients have been mixed,
the operator takes a sample that is analysed for fat content. Based
on the result of the analysis, the operator adjusts the mixture by
adding a calculated amount of fat-containing raw material. After
renewed mixing, a new sample is taken and analysed. The result of
this analysis will normally fulfil the specifications, so that all
that now remains is to complete the mixing process.
The method requires much time and effort to ensure that the
finished product complies with the specifications. Even then, the
content of the various ingredients in the finished product will
vary considerably within the limits of the specifications, so that
in may cases, the product will lie relatively far from the optimum.
If adjustments and mixing operations have to be repeated too often,
problems with so-called "overmixing" can arise, manifesting
themselves as formation of fat smears and exudates, impairing the
quality of the product. In many establishments, however, the method
is preferred, as it is flexible and makes it possible to use the
raw materials in their original state and without having to analyse
them.
The indirect method consists in that each and every batch of raw
materials is analysed for its content of fat, protein and water. In
other words: from each and every container or tub containing raw
material, samples have to be taken and analysed. After this, the
results of the analyses are used to calculate the quantity of each
type of raw material to be used for producing a finished product
with predetermined specifications. The calculation is preferably
carried out using a special computer program, as it may be
necessary to use 5-10 different types of raw materials. If all
instructions are followed, the finished product will comply with
the specifications.
This method tends to be preferred by an increasing number of
establishments, as it makes it possible to avoid "overmixing" and
to come closer to the optimum composition or to comply with
stricter specifications.
With both methods, the fat content is determined by means of one of
the usual methods of analysis in the meat-processing industry, of
which some are carried out "at line", i.e. by the operator in the
processing room, and some "off line", i.e. by an assistant in a
separate laboratory. The first type of methods of analysis
comprises the determination of fat by means of X-ray (Anyl-Ray) and
determination of specific weight (Scanalyser). The latter type
comprises wet chemical analysis, Fosslet analysis, NIT-transmission
measurement (Tecator) and NIR-reflection analysis.
Both of these methods require the operator to be skilled in taking
a sample that is representative of the full amount of material.
U.S. Pat. No. 4,844,619 (Weiler & Co.) discloses a specially
designed mixing machine provided with a device for taking samples
to be analysed for their fat content. The machine comprises an
elongate mixing tub and a worm conveyor placed in a longitudinal
recess in the bottom of the tub. The worm serves to move material
from one end of the tub to the other end during the mixing process.
When the worm rotates in one direction, it can also convey new raw
material into the tub, while with the opposite direction of
rotation, it can convey a fully mixed meat product out of the
tub.
The device for taking samples is placed below the mixing tub and is
constructed like a meat mincer with a worm. Meat material from the
recess in the mixing tub falls down into the meat mincer, and the
latter advances it against a perforated disc with a rotating knife,
finally mincing the material to a suitable particle size. When the
material in the mixing tub is to be analysed, the meat mincer is
started and a suitable quantity of finely minced sample is
collected at the end of the mincer. The fat content of the sample
is determined in a separate measuring equipment operating by means
of X-rays.
With this mixing machine it is not required that the operator is
skilled in taking a representative sample. The sample, being
automatically taken out and finely minced by means of the meat
mincer, should be representative of the material in the mixing tub,
because the worm conveyor in the recess in the tub causes the
different raw materials to be mixed with each other.
U.S. Pat. No. 4,171,164 (The Kartridg Pak Co.) discloses a system,
in which meat without fat and meat containing fat, respectively,
are introduced into a mixing tub in proportions giving a certain
percentage of fat in the product in the tub after mixing. The
system may comprise two separate lines, each advancing a respective
type of raw material to the mixing tub.
Firstly, the raw materials are coarsely comminuted to a particle
size of 10-15 mm, and are then pumped to respective measuring
devices, using dual-energy X-ray for continuously determining the
fat content in each type of raw material. After this, the material
flow of each type of raw material is measured by means of hopper
devices collecting material and acting upon some weighing cells.
Finally, the two types of raw material are introduced together in
the mixing tub. The percentage of fat in the mixing tub may be
computed continuously based on the measuring results. The ratio
between the flow of the two material streams is controlled so as to
finally achieve a mixture with a predetermined percentage of fat.
E.g., the pump in one of the lines can run with a constant output
and the pump in the other line with a varying output depending on
the instantaneous and integrated measuring results.
The raw materials having been introduced together in the tub are
mixed to form a homogeneous mass that is discharged into a hopper
and finely minced to the desired product, e.g. sausage meat.
This system requires a considerable quantity of equipment to be
provided and maintained. Further, it is based upon the material
passing unchanged through the analysis and on measuring all the
material. These conditions can only be met by extremely few methods
of analysis.
SUMMARY OF THE INVENTION
It is the object of the present invention to provide a method of
the kind referred to initially, with which it is possible to
determine the content of one or a number of components of a
material being mixed in a container by automatically taking and
analysing samples, said method also making it possible to determine
whether the material in the container has been mixed into a
homogeneous mass. It must also be possible to use the method, even
if the size of an automatically taken sample is less than the
representative quantity required to determine the content of the
components with the desired accuracy, said representative quantity
when operating with meat products of the types described above
usually constitutes 5-10 kg.
The above object is achieved by the method according to the present
invention, which is characterized in that
material is removed from the tank through a tube situated adjacent
to the tank and communicating with the internal space of the
tank,
the material having been removed is moved to a segment of the tube
adapted for making measurements,
the effect caused by the material placed in said tube segment on
electromagnetic energy made to enter the tube is measured,
the above steps a-c, possibly comprising the introduction of
completely or partly new material in the tube segment, are repeated
once or a number of times, and
the individual measurement values or sets of same from the
individual measuring procedures are registered.
With the method according to the present invention, it is not only
possible to determine automatically the content of components in
the material, but at the same time it is also possible to monitor
the mixing process and to use relatively small samples, i.e.
considerably less than the 5-10 kg required when processing
coarsely comminuted meat products. Thus, the method according to
the present invention exhibits substantial advantages as compared
to the methods used at the present time.
The taking of samples and the analysis of the material in the
mixing tank may be carried out automatically. The method does not
require operators to be skilled in taking representative samples of
the material. The determination of e.g. the fat content in meat
products being mixed may take place as often as desired, and every
time, the sample is taken from the mixing tank in the same manner,
thus contributing to improving the reproducibility. The equipment
does only have to be dimensioned for relatively small samples,
because the taking and measuring of samples are merely repeated,
until the sum total of the measurements is representative and
provides the desired accuracy. In other words: the mechanical parts
may be small, and the volume of material used for measurement in
each cycle may be chosen to be the optimum for the measuring method
being used.
The content of components in the material can be monitored during
the whole mixing operation by automatic and repeated sampling and
analysis, and it is possible to determine when the material has
achieved the requisite homogeneity. A novel feature within this
field is that the mixing process may be interrupted as soon as the
material has been sufficiently and thoroughly mixed.
When carrying out the method according to the present invention it
is possible to use the mixing equipment already installed in the
establishments. All that is required is to provide them with a
device for taking samples and making analysis.
It is clearly an advantage to carry out the analysis directly on
the material being mixed instead of on each and every batch of raw
material as in the previously known indirect method referred to
above. Meat having been processed at other locations in the same
establishment can, after being comminuted, be used directly in the
mixer without first having to analyse it and keep it separate from
other batches. There is also no need for accurate weighing of the
quantities of meat introduced in the mixing tank or for use of
complicated and costly data-processing programs for adjusting the
percentage of fat. Re-examination is unnecessary.
If desired, the raw materials may be introduced a number of times
in succession, e.g. if a pre-mix of two raw materials is to be
produced first, and then a finished mixture is to be produced by
adding a third raw material. This fact may e.g. be exploited if the
finished mixture is to contain two components that the measuring
method is unable to distinguish from each other. If e.g. a sausage
meat with a certain proportion between pork and beef is desired, a
pre-mix having the correct ratio between pork and fat may be
produced, after which beef and fat can be added until the mixture
with the desired composition has been produced.
The method according to the present invention may be used in
connection with the mixing of fat-containing meat raw materials,
but it is possible to use it with the same advantages with others
of the flowable materials referred to, whether these are in the
form of particles or liquid.
Materials of interest are e.g.:
vegetable foods, such as wheat, barley, rye, maize, rice, coffee
and cocoa in the form of whole grains or milled product (analysis
for protein, starch, carbohydrate and/or water), seeds, e.g. peas
and beans, such as soya beans (analysis for protein, fat and/or
water), products mainly consisting of or made from vegetable raw
materials, such as snacks, dough, vegetable mixtures, margarine,
edible oils, fibre products, chocolate, sugar, syrup, lozenges and
dried coffee extract (powder/granulate),
animal foodstuffs, such as dairy products, e.g. milk, yoghurt and
other soured milk products, ice cream, cheese (analysis for
protein, carbohydrate, lactose, fat and/or water), meat products,
e.g. meat of pork, beef, sheep, fowl and fish in the form of minced
or emulgated products (analysis for protein, fat, water and/or
salts) and eggs, all in more or less frozen condition,
fodder, e.g. pills or dry/wet fodder mixtures of vegetable
products, fats and protein-containing raw materials, including pet
food,
pharmaceutical products, such as tablets, mixtures, creams and
ointments.
A particular embodiment of the method according to the present
invention comprises that the material being present in the tube
section during a measurement constitutes a quantity not being
representative for determination of one or a number of components
of the material in the tank on the basis of a recorded measuring
value or set of same, and that the content of one or a number of
components of the material in the tank is determined by repeating
steps a-d of claim 1 so many times with introducing new material
into the tube segment, that the sum total of the quantities of
material being successively introduced into and measured in the
tube segment constitutes a representative quantity, after which the
content of the component or components concerned is computed on the
basis of the measuring values or sets of same having been
registered.
The sample-taking and analysis should preferably be carried out in
a non-destructive manner and allowing the sample material to be
returned to the tank unharmed. For this reason, the method of the
invention is preferably carried out by the material, which with
regard to components and size of any particles is substantially
unchanged relative to the material in the tank, being introduced
into the tube segment, and that when the measurement has been
carried out, said material is returned to the tank at a distance
from the opening serving for removing material from the tank.
Advantageously, the method is performed by the removing of material
from the tank, the moving of the material having been removed from
the tank to the segment of the tube and the measurement of the
effect caused by the material on electromagnetic energy is
performed while the material is being treated in the tank by means
of the mixing devices, whereby it is possible to save time and
possibly to facilitate the taking of samples from the tank.
By performing the measurements while the material in the tube
segment is at rest, it is possible also to use measuring methods
requiring relatively long measuring periods.
Material present in the tube segment and containing air or gas is
compressed, preferably to a pressure of between 200 and 2000 kPa (2
and 20 bar), before the measurement is carried out. Hereby air
bubbles possibly being present in the material will be compressed
or dissolved so as normally to improve the measuring accuracy and
simplify the measurement.
For measuring the properties of a sample it is possible to use
different types of electromagnetic energy, preferably by the use of
electromagnetic energy in the form of microwaves of frequencies in
the interval between 300 MHz and 300 GHz, single-energy,
dual-energy or multi-energy, X-ray or near-infra-red radiation.
The designation "near-infra-red spectroscopy" (NIR) is used for
measuring methods being based upon the interaction between matter
and electromagnetic radiation in the wavelength interval from 700
to 2,500 nm. The reason for using this designation is that it
covers that part of the infra-red wavelength interval lying closest
to the visible spectral interval of 400-700 nm. In the literature,
the designation "near-near-infra-red interval" (N.sup.2 IR) is used
for electromagnetic radiation with wavelengths from 700 to 1,200
nm.
Meat consists substantially of water, protein and fat. Each type of
chemical bond, e.g. O--H, C--H, C.dbd.O, C--N, N--H, absorbs light
at wavelengths being characteristic of the particular part of the
molecule. The absorption is caused by two different atoms being
bonded to each other functioning as an electric dipole receiving
energy from the electric and magnetic fields in the radiation,
causing the group of atoms to vibrate. The light absorbed by a
C.dbd.O bond in a triglyceride will have a wavelength differing
from that absorbed by a C.dbd.O bond in a protein molecule. By
measuring the attenuation of light passing through a sample of meat
and having one of these characteristic wavelengths it is possible
to determine the percentage of a component of the meat.
Measurements in the near-infra-red interval may be carried out in
two ways, either by transmitting light through the sample
(near-infra-red transmission, NIT) or on the basis of the
reflection from the surface of the sample (near-infra-red
reflection, NIR). In samples with a high content of water, such as
meat, NIT cannot be used with measurements above 1,300 nm, because
the absorption in the water molecules is far too high at longer
wavelengths. If an Si-detector is used, it is only possible to
operate at shorter wavelengths than approx. 1,050 nm, since this
type of detector is insensitive at longer wavelengths.
Reflection measurements have the disadvantage of having to be
carried out through a quartz-glass window, since ordinary glass
does not allow much near-infra-red light to pass through. It cannot
be avoided that fat from the coarsely comminuted meat adheres to
the inside of the quartz-glass window, thus possibly causing
erroneous measurements. Further, a reflection measurement will not
be as representative as an NIT-measurement, because the volume
being measured is small.
For this reason, optimum conditions for measuring are achieved by
carrying out near-infra-red measurements by transmission through a
physical path length in the measuring tube of e.g. 50-60 mm. The
sample preferably remains stationary during that fraction of a
second, during which the measurement is carried out. The sample
should be as free from air pockets as possible, and this is
achieved by compressing the sample.
The near-infra-red radiation may be detected by using the following
materials:
Si: A highly sensitive and cheap type of detector, used in the
interval 400 to 1,100 nm.
Ge: Hardly as sensitive as Si, but may be used from 800 to 1,800
nm.
InGaAs: only half as sensitive as Si, but reacts very quickly and
may be used from 800 to 1,760 nm.
PbS: Low sensitivity, but is cheap and may be used from 650 to
10,000 nm. Temperature stabilization is required.
PMT (Photo-Multiplier Tube): This is by far the most highly
sensitive type of detector.
Measurements on natural products have shown that there is no linear
correlation between the absorption of light and the percentage of a
compound in the sample. The absorbance is not only due to the
presence of absorbent compounds in the sample, but is also
influenced by the dispersion of light in the sample. Further, it
must be taken into account that the composition of natural products
is so complicated, that absorptions caused by different compounds
or functional groups overlap each other in the spectrum. For this
reason, it is necessary in this connection to use more complicated
mathematical models, e.g. neural networks or classical statistical
methods, for determining the content of a compound in the
sample.
Tests with comminuted meat raw materials on an NIT-analysis
instrument have shown that it is possible to determine the three
main components fat, water and protein, even in a situation in
which they do not add up to 100% due to other additives.
X-rays are electromagnetic radiation that is dispersed and
attenuated by interaction with matter. The radiation is produced by
an X-ray source consisting of an electron accelerator and an anode,
against which the accelerated electrons are made to impinge. With
X-rays, the dispersion and attenuation taking place during the
passage of the beam of radiation through a substance increases
markedly with an increase of the number of electrons in the
substance capable of interacting with the radiation. The variation
in the interaction is especially marked in the vicinity of
particular energies, the so-called "absorption edges".
For a long time, X-rays have been used to measure the composition
of a mixture, and absorption spectra for a series of substances are
known. The difference between the mass attenuation coefficient for
fat (fatty tissue) and protein/water (meat) may be measured at
energies from approx. 0 to 100 keV. In this interval, it is
possible to use X-rays for determining the percentage of meat and
fat in a material.
If possible, single-energy X-ray measuring equipment is preferably
used. When the meat product contains air, dual-energy X-ray
equipment is used, as the high energy may be calibrated for
measuring the specific weight. The measurements may be carried out
continuously or based on discrete counts. In both cases it is
necessary to use highly collimated radiation, which causes a
substantial reduction of the measuring volume. In order to measure
a representative volume it is frequently necessary to carry out a
very great number of measurements.
It may be advantageous to carry out measurements with successively
changing energies in order to increase the dynamic range and
contrast of a system for measuring fat.
X-ray windows may consist of a light material, e.g. epoxy. The
capacity of an individual measurement with an X-ray window of
maximum size may be 150 cm.sup.3.
Microwaves are electromagnetic waves behaving as if consisting of
electrical (E) and magnetic (H) waves. The depth of penetration and
propagation velocity of the waves are different in different
substances. This difference is exploited for measuring components
of foodstuffs. When measuring according to these methods, the
energy level is so low that the sample is only slightly heated.
At the present time only one apparatus capable of measuring the fat
content in comminuted meat is known. This apparatus has been
developed by Torry Research Station in Scotland and is adapted to
measure the attenuation of microwaves transmitted along the surface
of the meat.
In an as yet not published series of tests with a microwave
measuring apparatus using transmission measurement, the fat content
in trimmings having been coarsely comminuted down to 3 and 10 mm
have been measured over a vide range (4-83% fat). The samples were
placed in a rectangular waveguide, and the transmission examined
using microwaves in the range 1.7 to 2.6 GHz. It turned out to be
possible to measure the content of meat and fat using three
different measuring principles: Attenuation, phase shift and time
delay. A substantial advantage of using transmission measurement as
compared with surface measurement is the possibility of using a
relative large measuring volume.
By combining an attenuation measurement with a phase-shift
measurement it is possible to provide a method that is insensitive
to variations in the specific weight of the samples. This means
that air bubbles in the sample can be ignored. A time-delay
measurement is advantageous if the dispersion of the waves is
unknown, the measurement being carried out on the direct wave
between the transmitter and receiver through the measuring object.
The time delay to the front edge of a received pulse may be
measured according to principles known in the field of radar
technology.
Microwaves may be unsuitable for measuring frozen or partly frozen
meat products, because the water molecules are unable to rotate
when in the solid state (ice). For this reason, microwaves are
hardly influenced by frozen products.
When carrying out the method according to the present invention,
the influence of the material on the electromagnetic energy is
preferably measured by measuring the attenuation, phase shift or
time delay of the microwaves in the tube segment in the shape of a
microwave waveguide, by measuring the attenuation of X-ray
radiation transversely through a material contained in the tube
segment, or by measuring the transmittance or absorbance of a
material contained in the tube segment in the near-infra-red
interval (NIT).
It is especially preferred that the transmittance or absorbance of
the material placed in the tube segment is measured at a number of
wavelengths in the interval between 700 and 2400 nm, especially
between 700 and 1200 nm, after which the content of one or a number
of components of the material is determined on the basis of the
measuring values or sets of same having been registered.
It has been found that NIT-measurement can be used for determining
the particle size in the material in the tube. If wanted, the
transmittance or absorbance of a particulate material positioned in
the tube segment may accordingly be measured at several wavelengths
in the range 700 to 2400 nm, especially 700 to 1200 nm and the
particle size of the material is determined on the basis of the
measuring values or sets of same having been recorded.
A special application of the method according to the invention
comprises that the measuring values or sets of same are used to
ascertain whether or when the mixture in the tank is sufficiently
homogeneous to allow the mixing process to be terminated and the
material possibly discharged from the tank or subjected to a
succeeding processing step. This makes it possible to avoid
problems with so-called "overmixing".
An embodiment of the method of the invention may be utilized for
adjusting the composition of the material in the mixing tank. This
embodiment consists in that the content of one or a number of
components of the material is determined on the basis of the
measuring values or sets of same having been registered, and that
the results or their deviation from desired values or information
about the need for adding material with a view to augmenting the
content of a component of the material in the tank to achieve a
desired value is/are shown on a display unit and/or used for
controlling a dosage control unit associated with the tank and
adapted to add a deficit quantity of a component to the material in
the tank.
A particularly preferred embodiment of the method according to the
invention comprises that the transmittance or absorbance of a
particulate material, e.g. a comminuted meat product with an
average particle size between 2 and 30 mm, is measured at a number
of wavelengths in the near-infra-red interval, preferably between
700 and 1200 nm, after which the measuring values or sets of same
having been registered are used
to determine the content of one or a number of components of the
material, e.g. in a meat product preferably its content of fat,
protein, collagen and/or water, and/or
to ascertain whether or when the mixture in the tank with regard to
one or a number of components is sufficiently homogeneous to allow
the mixing process to be terminated and the material possibly
discharged from the tank or subjected to a succeeding processing
step.
This makes it possible to control or determine a number of
different parameters of substantial importance for a satisfactory
mixing process.
The present invention also relates to a plant for mixing an
inhomogeneous flowable food material, fodder material or
pharmaceutical material, and comprising a tank for the material
provided with mixing devices, the plant being characterized by
further comprising, situated adjacent to said tank, an examining
unit comprising a tube having an opening communicating with the
internal space of the tank for removing material from the latter,
in said tube, a conveying member 18 for conveying material having
been removed through said opening into a segment of said tube
adapted for carrying out measurements, a measuring device situated
adjacent said segment of said tube and adapted to transmit
electromagnetic energy into said segment and to measure the
influence on this energy exerted by the material being present in
said segment, a control unit to cause the measuring procedure
comprising the introduction of completely or partly new material in
said segment and measuring of its influence on electromagnetic
energy, to be repeated, and a recording unit connected to said
measuring device and adapted to record individual measurement
values or sets of same for material having been measured in the
respective measuring procedures.
The measuring device preferably comprises a light source on one
side of said tube segment and a light receiver on the opposite
side, and that the walls of the tube segment lying in the path of
rays between the light source and the light receiver consist of a
material that is at least translucent for the wavelength interval
of the light to be examined, depending on the flowable material, on
which measurements are to be carried out.
An embodiment of the plant is characterized in that the light
source and the light receiver are of the wide-spectrum type, and
that a rotatable filter disc is placed in the ray path between the
light source and the light receiver, said filter disc having a
number of filters situated at equal distances from the axis of
rotation of the disc and each adapted to allow rays of a respective
wavelength interval to pass, a motor on the shaft of said disc
being adapted to bring one filter at a time into the path of
rays.
A preferred embodiment consists in that a number of monochromatic
light sources, each adapted to emit light in a respective
wavelength interval, is situated on one side of said tube segment,
and that a light receiver is situated on the opposite side of said
tube segment.
Hereby between 4 and 20 monochromatic light sources in the form of
laser diodes may be situated on one side of said tube segment and
adapted to emit light, each in a respective wavelength interval
within the region between 700 and 1200 nm.
Further, the present invention relates to an apparatus for taking
samples for use in the plant according to the invention in
connection with the examination of a flowable material. The
apparatus is special by comprising a tube comprising an opening for
receiving the material to be examined and a tube segment adapted
for carrying out the examination, a movable closure member situated
in said tube close to the opening for receiving material, and a
conveying member to convey material having been received into the
tube segment adapted for carrying out of the examination. Using
such an apparatus, it is possible to take a sample directly out of
the mixing tank and place it in the measuring space of an analysis
equipment.
The closure member may be adapted to be opened in connection with
the reception of material and to be closed in connection with the
conveying of material having been received into said tube segment
adapted for carrying out the examination. This embodiment prevents
the material from flowing backwards.
The apparatus may comprise a second closure member in the tube on
the side of said tube segment opposite said receiving opening, said
second closure member being adapted to be closed for a period while
the conveying member conveys fully or partly new material into said
tube segment adapted for carrying out the examination, and to open
when the material having been examined is to be moved out of said
tube segment. Hereby it is possible to compress the material during
the measurements and to express it from the measuring region when
the measurement has been carried out.
Preferably said conveying member is a plunger slidable in a
fluid-tight manner along the inside of said tube. Hereby the smear
problems known from worm conveyors, which can give a film of fat on
the windows which is disturbing for the measurement, are prevented
to a high degree.
Preferably the apparatus comprises one or a number of pneumatic
cylinders with associated pistons adapted to actuate said conveying
member and/or closure members in said tube.
As mentioned, it has been found that the particle size of flowable
material may be determined using NIT measurements. For this reason
it is also possible, if so desired, to carry out a particle-size
determination, by measuring the transmittance or absorbance of a
sample of the material placed in the tube segment at a number of
wavelengths in the near-infra-red range (NIT), and to determine the
particle size of the material by comparing the set of measuring
values having been obtained with corresponding data sets for
materials with a known particle size or by inserting the measuring
value set in an algorithm provided on the basis of data sets for
materials with known particle sizes.
Thus, it is e.g. possible to determine the particle size of a
material in a mixing tub or tank or to determine whether two raw
materials having different particle sizes have been mixed
sufficiently thoroughly.
The representative quantity necessary for determining the
percentage of a component, e.g. fat, can vary with the size of the
particles. When the particle size is known, it is possible to
calculate the representative quantity, and based on this value it
is possible to determine how many times the sampling and measuring
cycle of the method according to the invention is to be repeated in
a plant, in which only small quantities at a time are being
examined. In this manner it is possible to carry out the measuring
procedure in the shortest possible time with a given accuracy, also
in those cases, in which the particle size of the material varies
considerably.
The measurements of the particle size may be repeated on fully or
partly new material being placed in the tube segment, and the value
of the particle size or of the deviation of the measurements from a
predetermined value having been found may be utilized for
continuous control or monitoring of a machine comminuting or
grinding the material. In this manner it is possible to use the
measurements for dynamic control of various processes.
It is possible to carry out measurements at a number of wavelengths
in the near-infra-red range between 700 and 1,200 nm. This is
preferred when working with meat products containing fat.
BRIEF DESCRIPTION OF THE DRAWINGS
In the following detailed portion of the present description, the
invention will be explained in more detail with reference to the
drawings, in which:
FIG. 1 shows an embodiment of a plant according to the invention
seen in elevation and partly in section,
FIG. 2 shows the plant seen from one of its ends,
FIGS. 3a-3f show an apparatus used in the plant for automatic
taking out samples and analysing these in a measuring equipment,
these figures showing the apparatus in various operating
positions,
FIG. 4 shows the transmittance at various discrete wavelengths of
samples of meat containing much and little fat as measured in the
measuring equipment,
FIG. 5 shows another embodiment of the measuring equipment in the
apparatus according to FIGS. 3a-3f,
FIG. 6 shows a third embodiment of the measuring equipment,
FIG. 7 shows a fourth embodiment of the measuring equipment,
FIG. 8 shows NIT spectra of two types of meat in two different
degrees of comminution, and
FIG. 9 is a classification diagram based upon a principal component
analysis of average spectra.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The plant of FIG. 1 comprises a conventional mixer 1 with a mixing
tank 2 capable of accommodating between 1,200 and 4,500 kg meat
material according to need. In the tank 2 there are two mixing
devices consisting of two mutually parallel shafts 3 with radial
rods carrying blades 4. The mixing devices can be rotated in both
directions by means of a motor arrangement 5. The arrangement is
controlled by means of a control panel 6, with which an operator
selects the mixing program suited for the work in hand.
In the end of the tank 2 opposite to that of the motor arrangement
5 there is a discharge opening equipped with a trap door 7 (FIG. 2)
adapted to be opened and closed by means of a pneumatic cylinder 8.
The bottom of the tank 2 is indicated with an arched dotted line.
During discharge, the material tends to collect in the deeper
left-hand part of the tank, here being "shovelled" towards the
discharge opening by the mixing device.
On one side, the mixing tank 2 carries a worm conveyor 9
constituting an additional facility for discharging material from
the tank. The worm conveyor 9 may be terminated in a perforated
disc with a rotating set of knives adapted to comminute the
material during the latter's discharge. EP-A-0,569,854 (WOLFKING
DANMARK A/S) comprises a description of a mixing machine of this
type.
In the embodiment being discussed, the tank carries on its wall an
apparatus for taking samples from the material in the tank and
analysing the samples (FIG. 1). A control unit 6a situated below
the control panel 6 is electrically connected to the apparatus. The
control unit 6a serves to control the functions of the apparatus
and to receive and process measurement data from the apparatus with
regard to an automatically taken sample, e.g. in the form of
signals expressing the fat content of the sample. Signal-wise, the
control unit 6a is connected to the mixer's control panel 6, so
that the processed data from the apparatus may be shown to the
operator or used for automatic checking and control of the mixing
program stored in the control panel 6.
The construction and functioning of the sample-taking apparatus
will be evident from FIGS. 3a-3f illustrating various operating
positions in a cycle comprising taking a sample from the tank 1 and
analysing it.
The apparatus comprises a tube 10 composed of three tube segments
10a, 10b and 10c connected to each other by means of flanges 11.
The lowermost and uppermost segments 10a and 10c are angular, so
that the tube 10 consists of a vertical central part and two
horizontal end parts. In the vertical wall of the tank 2 shown to
the left in FIG. 1, an opening is cut close to the bottom, said
opening fitting the lower, horizontal end part of the tube, and at
a level above the shaft 3 a second opening is cut to fit the upper,
horizontal end part of the tube. By means of flanges 12 on the end
parts, the tube 10 is secured to the tank 2 opposite the openings,
so that material automatically flows into the lowermost tube
section 10a and may be returned to the tank by means of a conveying
device in the tube.
On the lower tube segment 10a, a cylinder 14, the lower end of
which is closed, is secured by means of a flange 13. In the
cylinder 14 there are two pistons 15 and 16. The upper piston 15
carries a short tube 17 capable of sliding within a lower, vertical
part of the tube segment 10a, while the lower piston 16 carries a
plunger 18 having an outside diameter corresponding to the inside
diameter of the short tube 17, so that the plunger slides within
the short tube. The black areas in FIGS. 3a-3f represent seals
providing sealing between mutually relatively movable parts.
A piston rod 19 is secured to the lower side of the piston 16 and
protrudes outwardly to the bottom of the cylinder 14. The piston
rod 19 comprises a duct 20 for compressed-air and a coupling part
21 for coupling to a compressed-air tube. For the sake of
clearness, compressed-air tubes and their connections to control
valves are not shown in the figures.
Through the duct 20, air under pressure may be introduced into the
interspace between the pistons 15 and 16, causing the piston 15 to
be forced upwards. Coupling parts 22 and 23 for connecting
compressed-air tubes are also formed in the bottom of the cylinder
14 and in the flange 13 constituting the top of the cylinder,
respectively.
The central part of the tube segment 10b serves as a measuring
chamber in connection with measurements of the transparency of the
meat material to infra-red light of various wavelengths. For this
purpose, the tube segment 10b comprises two windows 24 of glass or
other transparent material inserted in mutually facing cut-outs in
the tube wall. The tube segment 10b carries a housing 25 containing
various devices for measuring the transparency of the material at
any time being present between the windows 24.
The upper tube segment 10c comprises a flange 26, on which is
mounted a cylinder 27 with a closed end. A piston 28 is slidable
within the cylinder, and on its right-hand side carries a plunger
29 slidable in the horizontal part of the tube segment 10c. In the
closed end of the cylinder 27 there is formed a coupling part 30
for a compressed-air tube, and the flange 26 comprises a similar
coupling part 31 for compressed air.
The functioning of the plant will now be described in detail.
Various types of un-analysed raw materials, coarsely minced and
then placed in respective storage tubs, are weighed out and placed
in the tank 2, in which they are mixed for a short period by
rotating the mixing devices. A PLC unit (not shown) controlled by
the control unit 6a actuates the valves on the compressed-air tubes
connected to the apparatus through the coupling parts 21, 22, 23,
30 and 31 in a manner causing the pistons 15, 16 and 28 to take up
the positions shown in FIG. 3a. After this, the mixing devices are
made to rotate in such a direction, that the material close to the
bottom of the tank 2 is moved towards the opening near the bottom
of the tank and is forced out through the opening and into the
lower tube segment 10a. In the figures, the material is represented
by dotted areas.
When the pressure of the material against the opening is at a
maximum, i.e. when a blade 4 is adjacent the opening, the following
sampling and measuring procedure is initiated:
Compressed air is admitted to the space between the pistons 15 and
16, causing the piston 15 with the short tube 17 to move upwardly
to an upper position, in which the top edge of the short tube 17
abuts against an internal ledge a short distance above the lower,
horizontal end part of the tube. In this position, shown in FIG.
3b, the short tube 17 confines the material having been forced into
the vertical part of the tube by the mixing devices, the tube
already having been closed at the top by the plunger 29.
Now, the material having been confined is compressed by air under
pressure being admitted into the space between the bottom of the
cylinder 14 and the piston 16 via the coupling part 22, causing the
piston 16 with the plunger 18 to move upwardly, thus reducing the
volume available to the confined material. At the same time, the
volume of the space between the piston 15 and the piston 16 is
reduced correspondingly, and the consequent pressure rise being
relieved by means of the duct 20 and a back-pressure valve placed
on the associated compressed-air tube and set to a predetermined
pressure.
During the starting-up of the plant, i.e. when carrying out the
first cycle, the vertical part of the tube 10 mainly contains air,
for which reason the piston 16 with the plunger 18 will move to an
upper position, in which the piston 16 abuts against the lower side
of the piston 15. When a few cycles have been carried out, the
vertical part of the tube 10 will, however, mainly contain meat
material and only a lesser proportion of air. This is the operating
situation now to be described.
In this operating state, the piston 16 with the plunger 18 will
only move to an intermediate position, of which an example is shown
in FIG. 3c. In this position, there is equilibrium between the
pressure in the confined material and the upwardly directed force
exerted by the piston 16. Compression takes place to a relatively
high pressure in order to reduce or eliminate the influence of the
air upon the measurement being carried out on the material between
the windows 24. With the transverse dimensions of the piston 16 and
the plunger 18 shown in the drawing, a pressure amplification of
five times is achieved, creating a pressure in the material of
1,250 kPa (12.5 bar), if the compressed air is set to a pressure of
250 kPa (2.5 bar).
After this compressing of the material in the vertical part of the
tube 10, measurements of the transparency of the material between
the windows 24 are carried out at a number of wavelengths in the
infra-red region, and the measurement results are used for
calculating one or a number of characteristic properties of the
material. The construction and the functioning of the measuring
equipment will be described in connection with the explanation of
FIG. 3d.
When the measurements have been carried out, the pressure in the
vertical part of the tube 10 is equalized to atmospheric pressure
by moving the piston 28 with the plunger 29 towards the left,
compressed air being admitted on the right-hand side of the piston
28 via the coupling part 31. When the vertical part of the tube 10
is opened at the top, material from this tube may expand outwardly
in the horizontal part of the tube in the tube segment 10c and
further out into the tank 2. As soon as the pressure falls in the
vertical part of the tube, the piston 16 with the plunger 18 is
moved towards its uppermost position shown in FIG. 3e, causing
further material to be discharged from the vertical part and forced
out into the tank.
When the piston 28 with the plunger 29 has reached the extreme
left-hand position, the piston is reversed towards the initial
right-hand position, compressed air being admitted on the left-hand
side of the piston 28 through the coupling part 30, the pressure on
the right-hand side of the piston being removed at the same time.
During the reverse movement, the plunger 29 forces material out
from the upper, horizontal part of the tube in the segment 10c and
back to the tank 2. In this manner, material having entered the
tube segment 10a through the opening close to the bottom of the
tank will be returned to the tank 2. During the reverse movement,
the plunger 29 will again close the vertical part of the tube 10 at
the top as will be evident from FIG. 3f.
After this, the piston 15 with the short tube 17 and the piston 16
with the plunger 18 will be moved towards their bottom positions,
pressure being applied to the upper side of the piston 15 via the
compressed-air conduit connected to the coupling part 23. During
the downward movement of the short tube 17 and the plunger 18 in
the vertical tube, the increase in volume creates a sub-atmospheric
pressure in the latter. During the final part of the movement of
the short tube 17, passage is provided between the vertical tube
segment 10b and the lower, horizontal end part in the tube segment
10a, so that material will be sucked into the vertical part of the
tube. The opening of this passage will preferably occur at the same
time as a blade 4 is opposite the opening near the bottom of the
tank, so that at the same time, suction will be applied to the
material from one side and pressure from the other. In this manner,
new material is moved into the tube segment 10a.
When the pistons 15 and 16 have reached their lowermost position,
and the piston 28 is in its extreme right-hand position (FIG. 3a),
a portion of material in the vertical part of the tube has been
ejected back into the tank and a new portion of material has been
taken in from the bottom of the tank for subsequent compressing and
measuring in the vertical part of the tube. At this point, one
working cycle has been completed. This cycle may immediately be
succeeded by new, similar working cycles in a given rythm, e.g.
each second (making the cycle time one second). The internal
diameter of the vertical part of the tube and the stroke volume of
the plunger 18 may e.g. be so dimensioned that each working cycle
will move 200-400 ml of new material into the tube. After one or a
few working cycles, the new material will have been introduced into
the space between the windows 24, after which the measurement may
be carried out.
By repeating the measurement on new portions of material being
introduced into the space between the windows 24, a sufficient
number of measurement data will eventually be obtained to make
their sum total representative, making it possible to determine the
fat content in the coarsely comminuted material with the requisite
accuracy. The quantity of material necessary to achieve
representative measurements will depend on the type and particle
size of the material. It should be determined for the materials
most commonly used, cf. example 1.
The measuring equipment in FIG. 3d will now be described in more
detail. It comprises a wide-spectrum light source 32 emitting light
within the working region, in the present case the near-infra-red
region between 700 and 1200 nm. The present embodiment comprises a
tungsten-halogen lamp emitting a major proportion of the electrical
energy supplied in the infra-red spectral region and having a
wattage between 20 and 70W.
Close to the light source 32, a preferably elliptical reflector 33
is placed in such a manner, that the light will mainly be directed
towards the right. A rotatable filter disc 34 is placed between the
light source 32 and the window 24 in the tube section 10b, said
disc comprising between 6 and 20, e.g. 12, different filters 35,
each allowing passage of light at a respective wavelength through
the windows 24 in the tube section 10b. The monochromatic light
entering through the left-hand window will suffer substantial loss
during the passage through the material in the tube, leaving the
tube through the right-hand window to strike a wide-spectrum
photo-detector 36, e.g. an Si wafer.
The attenuation of the light in the material is due to the
absorption caused by the various components in the material as well
as the dispersion and reflection of light caused by phase
transitions or particles in the material. The absorption depends on
the components and the wavelength.
Thus, the photo-detector 36 will produce signals depending on the
content of components in the material being examined and the
wavelength. The signal is amplified, filtered, digitized and stored
in an electronic memory. The windows and the path of the light beam
are dimensioned in such a manner, that the detector 36 receives
light having passed through a volume of material of more than 100
ml. The volume of material corresponds to the volume of the space
between the windows 24.
The measuring equipment comprises a step motor 37 for rotation of
the filter disc 34 to bring the filters 35 one by one into the path
of the light beam between the light source 32 and the detector 36.
Each time a new filter has been placed in a measuring position, the
signal from the detector 36 will be registered and stored, the
strength of this signal depending on the absorption of the material
concerned in the wavelength region of the filter. When measuring
values have been registered and stored for all filters in the disc
34, the measuring process is complete. The removal of material from
the region between the windows 24 can then be initiated by opening
the top of the vertical part of the tube.
FIG. 4 shows the signal from the detector 36 during one rotation of
the filter disc 34. The upper curve represents a finely minced
sample of pork meat with a fat content of approx. 50%. The sample
is placed in the tube segment 10b. The lower curve has been
recorded with a finely minced sample of beef with approx. 5% fat.
The samples attenuate the light approx. 4000 times. The peak values
of the curves represent the transmittance at the 11 different
wavelengths. It will be seen that the samples attenuate the light
differently at the different wavelengths due to the different
content of fat and water in the samples, this being used for
calculating these values.
By means of the measuring values stored, the data unit 6a will
automatically compute the content of e.g. fat in the material, a
program with the necessary computing routines having been read into
the unit. When working with coarsely comminuted meat material as
described, a single result is not sufficiently reliable, and for
this reason it is necessary to repeat the sampling and measuring
cycle a number of times, e.g. 10 times, until it is possible to
compute a sufficiently reliable value of the fat content on the
basis of the sum total of the measurement values or results.
If the material is homogeneous, e.g. in the case of finely
comminuted meat or meat emulsions, satisfactorily accurate results
may be achieved already by carrying out a single measuring
cycle.
Using the stored measuring values, it is possible to determine the
content of various components in the material, e.g. fat, protein,
collagen and water. If a number of sets of measuring values
produced from respective sampling and measuring cycles are used, a
substantial improvement of the accuracy of the results will be
achieved, this especially being of importance when the portion
being measured in each cycle is not representative.
Further, the measurement values from each sampling and measuring
cycle may be used for ascertaining whether the mixing procedure is
carried out in an optimal manner. Thus, the fat content of the
material may be computed for each sampling and measuring cycle, and
the result compared to the previous result or the average of a
number of immediately preceding results. If a large deviation is
found, this signifies that the material in the tank is still
inhomogeneous and that the mixing operation is to be continued. If
the deviation is only quite small or below a certain limiting
value, the homogeneity of the material cannot be improved by
continuing the mixing operation, for which reason this operation is
terminated. In this manner, it is normally possible to reduce the
duration of the mixing operation to the strictly necessary, and the
further mechanical working of the material is avoided.
Instead of the deviation, it is possible to use the standard
deviation of the results for controlling the duration of the mixing
operation. If the computed standard deviation for the most recent
cycles falls below a certain level, or if it is not improved by
continuing the mixing operation, this signifies that the mixing
operation is to be terminated.
Already before the material has become as homogeneous as desired,
it is possible in many cases to determine the fat content or the
like with a satisfactory accuracy, e.g. on the basis of the
tendency of the results to approach a final value. Thus, it can be
possible relatively early in the mixing operation to predict the
amount of fat-containing meat to be added to the material in the
tank to make the material resulting from the complete mixing
process comply with the specifications. Because of this, the method
and the plant make it possible to adjust the composition of the
material rapidly, this contributing to ensure that the material is
not subjected to mechanical working longer than what is necessary
to achieve a homogeneous mixture. When, by means of the
measurements, it is possible to ascertain that the material in the
tank exhibits the desired homogeneity, a final check of the fat
content may be made on the basis of the measurement results from
the most recent measuring cycles.
Obviously, it is possible to adjust the composition of the material
concurrently during the mixing operation by adding fat-containing
material, making it possible for the end product to comply with
strict specifications or be close to an optimal fat-content within
given specifications without necessarily increasing the mixing
time. The adding of fat-containing material in connection with the
adjustment may be carried out manually or automatically.
All these computations and evaluations may be carried out
automatically by the data unit 6a on the basis of the measurement
data received. When, aided by a program having been read in, this
unit e.g. ascertains that the results are stable, it can
automatically send a signal to the control panel 6 that the mixing
operation is completed with regard to homogeneity, after which the
control panel 6 itself or an operator receiving a signal from the
panel can stop the motor arrangement driving the mixing
devices.
In the present embodiment measurements are carried out using
near-infra-red radiation. The material being advanced in the tube
10 may, however, be examined using other types or a number of
different types of electromagnetic energy. E.g. downstream of the
tube segment 10b, a further tube segment may be inserted having
measuring devices for determining the material's content of water
in the liquid phase by means of microwave energy. In this case, the
material's ice content may be determined as the difference between
the water percentage determined with near-infra-red measurement in
the tube segment and the water percentage being determined using
microwaves.
Instead of a wide-spectrum light source behind a filter disc it is
possible to use discrete monochromatic light sources, each
admitting light at a respective wavelength. FIG. 5 shows such an
embodiment, utilizing laser diodes instead of the lamp and the
filter disc. The embodiment of FIG. 5 possesses the advantage of
having no moving parts.
The embodiment comprises a series of (high-power) laser diodes 40,
each radiating light of a predetermined wavelength inwards against
the material sample. Typically, 4-20 diodes situated on the same
chip, are used. Each laser diode emits light of a unique wavelength
within the region 800-1050 nm, making it unnecessary to use
filters. For measuring the light having passed through a sample of
a thickness 5-10 cm, a PMT detector 41 is used. By activating one
of the diodes 40 at a time, the detector 41 is used to measure how
much light penetrates the sample at the various wavelengths.
FIG. 6 shows an embodiment of a measuring device based on the use
of X-rays. The measuring device comprises an X-ray source 50 of 50
kV, a filter 51 and an adjustable aperture 52. Further, the device
comprises a radiation-receiving part in the form of a radiation
trap 53 and a detector 54, of which the latter may be a usual
detector or a fluorescent screen, the light emitted by the latter
being registered by a CCD camera 55. The tube 10 comprises two
beryllium windows 56 allowing passage of X-rays. The thickness of
the meat raw material in the tube 10 is e.g. 6 cm. The material is
compressed under a pressure of 13 bar, so that in practice it may
be regarded as a mixture without air pockets. At this pressure,
more than 3% air in the mixture is needed to cause a measuring
error of more than 0.5%.
The focus-detector distance of the X-ray source 50 is 25 cm, and
after passing through the 6 cm of meat material, the radiation has
a strength of approx. 1.6 mGy/mA min., which may be measured with a
good degree of certainty. The uncertainty where measuring with a
10.times.10 mm detector is 0.01% when measuring in 1 second, which
means that the measuring uncertainty is insignificant. (The
variation when determining fat percentage is a different matter, as
in this case, the physical properties of the material will be
important.).
The equipment may also be used for measuring partially frozen goods
without substantial changes in the measurement results. If,
however, measurements are carried out on salted raw materials, an
increased attenuation of the X-ray radiation will occur
corresponding to an increase of 1% of the meat percentage for each
percent by weight in NaCl. For this reason, the percentage of salt
must be approximately known in this case.
FIG. 7 shows a measuring device for measuring properties of
material in the tube 10 by means of microwaves. The device
comprises a microwave generator 60, a microwave detector 61 and a
waveguide 62 having a cage 63 between the generator 60 and the
detector 61. The holes in the cage 63 have a diameter of e.g. 10%
of the wavelength being used, so that the microwaves cannot escape
from the waveguide 62. The diameter of the holes is preferably at
least equal to the size of the particles in the coarsely comminuted
meat material. The meat material is forced through the cage 63 in
the vertical direction as indicated by the arrows. Glass windows 64
aligned with the walls of the tube 10 prevent the material from
entering the regions of the generator and the detector. The glass
windows 64 cause practically no attenuation of the microwaves
passing through them.
The microwave generator 60 emits energy at a fixed frequency and a
constant power of 1-10 mW. The energy being received by the
microwave detector 61 will vary with the fat content in the
material between the windows 64 and will be transformed into a
voltage being transmitted to the data unit 6a for further
processing.
The measuring equipment has a high capacity.
EXAMPLE 1
Necessary Repetition Factor for Representative Sample
In order to provide the requisite accuracy when determining the
content of fat, protein, water, etc., it is necessary to ascertain
whether the quantity being taken out as a sample in each cycle is
representative of the total quantity of meat in the mixing tank
and, if this is not the case, how many times the cycle is to be
repeated to achieve values that are representative of the total
quantity of meat (e.g. 1200 kg).
For examining this relationship a program has been developed to
simulate the taking of samples from the mixing tank. The program is
based on a number of assumptions about the nature of the coarsely
comminuted meat in the mixing tank and about the size of the sample
relative to the total quantity of meat. The following assumptions
are used in the program:
total quantity of meat in the tank: 1000 kg
weight of sample: 0.5, 1, 2, 5 and 10 kg
meat comminution degree: cubes with sides measuring 10 and 20 mm,
respectively (corresponding to a particle volume of 1 and 8
cm.sup.3, respectively)
average fat content: varying between 10 and 50%
variation in cube volume: 20% of the average cube volume, i.e. that
95% of all 1 cm.sup.3 cubes lie between 0.4 and 1.6 cm.sup.3
variation in fat content from cube to cube: 20%, but min. 0.8% fat
and max. 85% fat, i.e. that in a mixture with 30% fat, 97.5% of all
cubes lie between 0.8 and 70% fat
air volume: 0%
The program functions in the manner that the sample volume and the
volume of material in the tank are composed of cubes selected at
random on the basis of the above parameters. Then, the fat content
in the sample volume may be compared to the fat content of the
material in the tank for different average fat percentages, sample
sizes and degrees of coarse comminution.
The table below indicates the RSD (residual standard deviation) for
various sample sizes and degrees of coarse comminution. The results
have been produced by letting the computer carry out ten samplings
from each of six mixtures with a fat content varying from 10 to
50%. RSD is a measure of the average deviation between the fat
content in the sample and in the material in the tank.
______________________________________ Coarse commi- Sample RSD
nution (mm) size (kg) (% abs.)
______________________________________ 10 .times. 10 .times. 10 10
0.11 5 0.19 2 0.33 1 0.43 0.5 0.81 20 .times. 20 .times. 20 10 0.61
5 0.73 2 1.30 1 1.39 0.5 2.3
______________________________________
A coarse comminution down to cubes of 10.times.10.times.10 mm gives
an RSD at 5 kg that is less than the error when measuring fat
content in the laboratory. With a coarse comminution down to cubes
of 20.times.20.times.20 mm it is necessary to take a sample of
substantially more than 10 kg to make the error less than the
laboratory error.
The results may also be read in the following manner: If a perfect
method of analysis is available, capable of determining the fat
content of the sample volume, the fat content having been
determined will in 95% of the cases differ less than twice the RSD
value from the fat content in the tank. With a sample size of 5 kg
of cubes 10.times.10.times.10 mm, the variation will be greater
than 0.38% in only 5% of the cases; this is fully acceptable with a
certainty of the analysis method of 0.5%.
If measurements are carried out in the plant on 125 ml material in
each cycle, these conditions will make it necessary to carry out 40
sampling and measuring cycles to obtain a representative value of
e.g. the fat content in the mixing tank with a certainty of
analysis of 0.5%. If a somewhat reduced certainty can be accepted,
the number of cycles may be reduced, e.g. to 10.
EXAMPLE 2
NIT Measurements on Pork with Varying Fat Content and Degree of
Coarse Comminution
The tests are to ascertain whether an NIT analysis requires a
complete comminution before measurements are carried out on the
material.
2.5 kg of each of the following products are procured from a
slaughterhouse: foreloin (fat content 9%), neck (fat content 24%)
and shoulder cuts (fat content 45%). These test portions are
coarsely comminuted to 13 mm by means of a cutter.
From each of the test portions 400 g are taken out and measured on
an NIT analysis instrument for laboratory use (model Infratec 1255
from Tecator). The NIT-instrument comprises five cups with sample
material. The effective sum total of the sample volume for the five
cups is 25 ml. Then, the material having been removed is returned
to the test portions and the latter comminuted to 10 mm. From each
type of test portion partial samples of 400 g are taken out and
measured on the NIT instrument. Further, the procedure is repeated
to provide measurements on meat material of 8.5 and 3 mm. Finally,
the test portions are analysed for fat content using traditional
laboratory analysis.
FIG. 8 shows two average spectra for shoulder cuts and foreloin
comminuted to 13 mm as well as two previously produced model
spectra for meat of 3 mm with similar fat content.
It can be seen from the Figure that spectra with the same
percentage of fat mainly differ only by the parallel displacement
along the Y-axis; this is of no importance for determining the fat
content, since this solely requires the use of the relative changes
at the various wavelengths. It can also be seen that the absorption
at 932 nm provides a clear indication of the fat content of the
sample.
The next step is to carry out a principal-component analysis (PCA)
of the average spectra for each of the three types of meat and each
of the five degrees of comminution, so that a total of 15 spectra
enter into the analysis. The result of this classification is shown
in FIG. 9.
It will be seen that the spectra form groups in two directions,
viz. a first direction indicating the fat content of the sample,
and a second direction approximately at right angles to the first
direction and indicating the degree of comminution. Thus, the
Figure shows that it is possible using NIT analysis to determine
both the fat content and the degree of comminution.
The invention has been explained in the above mainly with reference
to the mixing of meat products, but it will be understood that the
invention may be used for measuring mixtures of materials, with
which electromagnetic radiation may be used to provide measuring
results containing information about the state of the mixture.
* * * * *